Lubricating composition for use in diesel engines compatible with biofuel

ABSTRACT

A method of operating a diesel engine comprises lubricating the diesel engine with a lubricating composition and using a biofuel as fuel, wherein the lubricating composition comprises a base oil belonging to Group III or Group II of the API base oil categories, from 0.5 to 5% by mass of a phenolic anti-oxidant, and from 0.5 to 5% by mass of an amine-based anti-oxidant, the total content of the anti-oxidants being at least 2% by mass.

RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No. 12/669807, filed 20 Jan. 2010, which is a national stage entry of PCT Application EP2008/059543, filed 21 Jul. 2008, which claims priority to Japanese Patent Application No. 2007-190658, filed 23 Jul. 2007, all of which are hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

This invention relates to lubricating compositions for use in diesel engines that use biofuels.

BACKGROUND OF THE INVENTION

In recent years, as a contribution to reducing CO₂ in the global environment, there has been increasing momentum towards making positive use of fuels derived from plants and produced through biomass technologies. However, in composition they are not necessarily similar to existing fossil fuels and so various problems that can be generated by biofuels may be expected. Various investigations are being made of techniques to cope with these in the lubricating oils used in internal combustion engines.

In the case of the alcohol fuels which are principally used in the field of gasoline engines, admixture with water cannot be avoided, and engine parts undergo a larger amount of wear than in the case of gasoline. Solutions for these problems have therefore been proposed. See Japanese Laid-open Patent 5-70786 (1993).

Biofuels for use in the diesel engines used in automotive vehicles have in some cases been produced by methyl esterification of plant oils, taking mainly rapeseed oil or sunflower oil as their raw material in France, German, and Italy within the EU, and mainly soybean oil as their raw material in the United States. In many cases, these fuels are used by mixing about 20% in a light oil.

There are several points about these biodiesel fuels which must be borne in mind when using them. They have aspects which demand improvement simply in fuel terms in that their viscosities and pour points are rather high, and they are prone to oxidise because, being derived from plant oils, they contain many unsaturated fatty acids. Furthermore, these biodiesel fuels may compete directly with edible vegetable oils, and so they have not been studied as much as the above-mentioned alcohol fuels as alternatives to gasoline, and there have hardly been any attempts to improve lubricating oils in association with biodiesel fuels.

In the above-mentioned diesel engines, because a mixture of biodiesel fuel with light oil is used, a phenomenon is seen whereby an unburnt portion of the biodiesel fuel becomes mixed with the lubricating oil, promoting ageing thereof. This creates difficulties for using the lubricating oil stably over long periods.

SUMMARY OF THE INVENTION

The inventors have discovered that it is possible to inhibit ageing, and in particular degradation of the detergent performance of the lubricating oil, even after admixture with biodiesel fuel, by combining different types of anti-oxidant, a phenolic anti-oxidant and an amine-based anti-oxidant, in the lubricating oil composition.

To this end, the present invention provides a lubricating composition for use in diesel engines compatible with biofuel, the lubricating composition comprising a base oil belonging to Group III and/or Group II of the API base oil categories, from 0.5 to 5% by mass of a phenolic anti-oxidant and from 0.5 to 5% by mass of an amine-based anti-oxidant, the total content of the anti-oxidants being at least 2% by mass.

According to this invention, it is possible to inhibit rapid degradation of the detergent performance and accelerated ageing of the lubricating oil, even after admixture of biodiesel fuel in the lubricating oil, by using different types of anti-oxidant, a phenolic anti-oxidant and an amine-based anti-oxidant, together, and thus it is possible to use the lubricating oil stably over a long period.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The light fuel oils and the biodiesel oils used in diesel engines of automotive vehicles, as already mentioned, have various obvious differences, and according to the literature (“New biomass liquid fuels for the 21st century”, published by the Kagaku Kogyo Nippo [The Chemical Daily] on 2002 Apr. 25, the teaching of which is hereby incorporated by reference) they can be summarised as being the differences shown in Table 1.

TABLE 1 Biodiesel oil Light oil Pour point (° C.) −5.5 −11.5 Kinetic viscosity (mm²/s) 5.6 3.0 Flash point (° C.) 135~145 88 Sulphur content (%) 0.0001 0.2 Carbon (%) 77.1~77.9 87.2 Hydrogen (%) 11.7~11.8 12.8 Oxygen (%) 11.1~11.2 0

As is evident from Table 1, among the aspects where biodiesel oils differ substantially from light oils is the content of constituent oxygen atoms. Also, it is believed that, since they contain double bonds derived from unsaturated fatty acids, the combustion reaction itself differs.

Further, it may be mentioned that, in terms of physical properties, the flash point is higher than in light oils and they are more prone to evaporate. When supplied as fuel to engines, the reaction may cease in the elementary process on the way to complete combustion, and the unreacted portion will often mix with the lubricating oil or the unburnt constituents themselves will be mixed with the lubricating oil, causing the formation of sludge in the lubricating oil and accelerating ageing of the lubricating oil through oxidation.

Given these facts, the lubricating oils will be characterised by being used under more rigorous conditions even than when exposed to high temperatures when using only light oils as the fuel.

For the base oils of this invention it is possible to use any suitable mineral oil or synthetic oil, and normally it is possible to use base oils, singly or in mixtures, that belong to Group III and Group II of the base oil categories of the API (American Petroleum Institute).

These Group III and Group II base oils include, for example, paraffinic mineral oils obtained by a high degree of hydrorefining in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil, base oils refined by the Isodewax process which dewaxes and substitutes the wax produced by the dewaxing process with isoparaffins, base oils refined by the Mobil wax isomerisation process, and the so-called GTL (gas-to-liquid) base oils solvent dewaxed or catalyst dewaxed after synthesis by the Fischer-Tropsch method. They include also those that may be designated as “synthetic oils” according to the rulings of the NAD (National Advertising Division) which is responsible for advertising adjudications in America.

Phenolic anti-oxidants and amine-based anti-oxidants are blended together in these base oils.

As examples of these phenolic anti-oxidants mention may be made of 2,6-di-t-butylphenol, 2,6-di-t-butyl-p-cresol, 2,6-di-t-butyl-4-ethylphenol, 2,2′-methylenebis(4-methyl-6-t-butylphenol), 2,2′-methylenebis(4-ethyl-6-t-butylphenol), 4,4′-bis(2,6-di-t-butylphenol), 4,4′-thiobis(6-t-butyl-o-cresol), and alkyl alcohol esters of 3-(4-hydroxy-3,5-di-t-butyl-phenyl)propionic acid such as 6 methylheptyl alcohol esters of 3-(4-hydroxy-3,5-di-t-butyl-phenyl)propionic acid.

Also, as examples of these amine-based anti-oxidants mention may be made of diphenylamines, p,p′-dioctyldiphenylamines, p,p′-dinonyldiphenylamines, p,p′-didodecyldiphenylamines, phenyl-a-naphthylamines, p-octylphenyl-α-naphthylamines, p-nonylphenyl-α-naphthylamines and p-dodecylphenyl-α-naphthylamines, and mixtures thereof.

One preferred example of the above-mentioned diphenylamines is a diphenylamine which is the reaction product of N-phenylbenzeneamine and 2,4,4-trimethylpentene.

The amount of the above-mentioned phenolic anti-oxidant is from 0.5 to 5.0% by mass based on the total amount of the lubricating oil composition, and preferably from 0.5 to 2% by mass.

The amount of the above-mentioned amine-based anti-oxidant is from 0.5 to 5.0% by mass based on the total amount of the lubricating oil composition, and preferably from 0.5 to 2% by mass.

For both the above-mentioned phenolic anti-oxidant and amine-based anti-oxidant, if the amount is less than 0.5% by mass the oxidative stability decreases, which is undesirable, and if it exceeds 5% by mass the piston detergency decreases, which is often undesirable.

The phenolic anti-oxidants and the amine-based anti-oxidants are used respectively in the above-mentioned amounts, but it is further required that the total amount of the two anti-oxidants at the same time is not less than 2% by mass. If the total amount of both is less than that, the expected effect will not be obtained.

It is also possible to add to this lubricating oil composition, as required, suitable dispersants, extreme-pressure agents, detergents, viscosity index improvers and other additives.

In another aspect the present invention provides a method of operating a diesel engine comprising lubricating the diesel engine with a lubricating composition according to the present invention and using a biofuel, preferably derived from rapeseed oil, as fuel.

EXAMPLES

The biodiesel fuel (BDF) was a methyl ester derived from rapeseed oil and was prepared so as to have the properties shown in Table 2.

TABLE 2 Characteristic Item Test method Units (numeric value) Density: vibration JIS K-2249 g/cm³ 0.883 method (15° C.) Flash point: PMCC method JIS K-2265 ° C. 155 Kinetic viscosity: 30° C. JIS K-2283 mm²/s 5.51 Cetane value JIS K-2280 53.0

The following constituent materials were used in preparation of the examples of embodiment and comparative examples.

-   -   (1) Base oil: a mineral oil belonging to API Group III     -   (2) Phenolic anti-oxidant: 6 methylheptyl alcohol ester of         3-(4-hydroxy-3,5-di-t-butyl-phenyl)propionic acid     -   (3) Amine-based anti-oxidant: diphenylamine being a reaction         product of N-phenylbenzeneamine and 2,4,4-trimethylpentene     -   (4) Additives package: additives containing dispersant, ZnDTP         and detergent.

Examples 1-4, Comparative Examples 1-6

Using the above-mentioned constituent materials, the lubricating oil compositions of Examples 1-4 and Comparative Examples 1-6 were prepared in accordance with Tables 3 and 4.

The above-mentioned Comparative Example 6 was a composition with a JASO (Engine Oil Standards Implementation Panel) DH-2 level diesel combustion engine oil for use in automotive vehicles.

The amounts of each constituent blended in are shown in each case as % by mass.

Tests

In order to view the performance of the lubricating oil compositions of Examples 1-4 and Comparative Examples 1-6, hot tube tests (according to JPI-5S-55-99; a standard test from the Japanese Petroleum Institute for determining high temperature deposits) were carried out at 280° C. under load conditions whereby 5% by mass of biodiesel fuel was added in respect of 100% by mass of each lubricating oil composition.

Evaluation of the hot tube tests was from 0 to 10 in fractions of 0.5, and 7 and above was set as the pass mark.

Test Results

The results are shown in Tables 3 and 4.

TABLE 3 Example Example Example Example 1 2 3 4 Base oil 86 85 85.5 82 Phenolic 1.0 1.5 1.5 2.0 anti-oxidant Amine-based 1.0 1.5 1.0 4.0 antioxidant Additives package 12 12 12 12 Total 100 100 100 100 Admixed BDF 5 5 5 5 Hot tube score 7.0 7.0 7.0 7.5

TABLE 4 Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Base oil 88 85.5 84.5 85.5 86.5 88 Phenolic 2.5 0.5 anti-oxidant Amine-based 2.5 3.5 1.0 antioxidant Additives 12 12 12 12 12 12 package Total 100 100 100 100 100 100 Admixed BDF 5 5 5 5 5 Hot tube score 1.0 2.0 5.0 3.0 2.5 7.0

Evaluation

When using a phenolic anti-oxidant and an amine-based anti-oxidant together, as shown in Examples 1-4, the amount of each being not less than 1% by mass and the total amount being not less than 2% by mass, an evaluation of 7 or higher was obtained in the hot tube test in all cases, and it was evident that these were lubricating oil compositions not prone to ageing after admixture of biofuel.

Anti-oxidants were not added in the case of Comparative Example 1, and the hot tube score was poor, 1.0. Comparative Example 2 used 2.5% by mass of only the amine-based anti-oxidant, and although the total amount exceeded 2% by mass the hot tube score was poor at 2.0. More amine-based anti-oxidant was added to Comparative Example 3 than in Comparative Example 2, but the hot tube score rose only to 5.0. Comparative Example 4 used 2.5% by mass of only the phenolic anti-oxidant, and although the total amount exceeded 2% by mass the hot tube score was poor at 3.0. Comparative Example 5 used both anti-oxidants together, but the total amount was less than 2% by mass and so the hot-tube score was poor at 2.5. A satisfactory effect was thus not obtained for any of Comparative Examples 1-5

Comparative Example 6 had no admixture of biofuel, and even though no phenolic anti-oxidant or amine-based anti-oxidant was used, the hot tube score was 7.0 and it can be seen that a satisfactory effect was obtained. 

What is claimed is:
 1. A method of operating a diesel engine comprising lubricating the diesel engine with a lubricating composition and using a biofuel as fuel, wherein the lubricating composition comprises a base oil belonging to Group III or Group II of the API base oil categories, from 0.5 to 5% by mass of a phenolic anti-oxidant and from 0.5 to 5% by mass of an amine-based anti-oxidant, the total content of the anti-oxidants being at least 2% by mass.
 2. The method according to claim 1 wherein the phenolic anti-oxidant is a 6-methylheptyl alcohol ester of 3-(4-hydroxy-3,5-di-t-butyl-phenyl)propionic acid.
 3. The method according to claim 1 wherein the amine-based anti-oxidant is a diphenylamine which is a reaction product of N-phenylbenzeneamine and 2,4,4-trimethylpentene.
 4. The method according to claim 1 wherein the biofuel used in the diesel engine is derived from rapeseed oil.
 5. The method according to claim 1 wherein the phenolic anti-oxidant is a 6-methylheptyl alcohol ester of 3-(4-hydroxy-3,5-di-t-butyl-phenyl)propionic acid and wherein the amine-based anti-oxidant is a diphenylamine which is a reaction product of N-phenylbenzeneamine and 2,4,4-trimethylpentene. 